Radiant tube heater and combustion air preheater therefor



Jan. 25, 1955 P. l..l KNIGHT 2,700,380

RADIANT TUBE HEATER AND coMBusTloN AIR PREHEATER THEREEOR Filed Dec. 29,1950 United States Patent() RADIANT TUBE HEATER AND COMBUSTION AIRPREHEATER THEREFOR Philip L. Knight, Toledo, Ohio, assignor to SurfaceCombustion Corporation, Toledo, Ohio, a corporation of Ohio AppiicationDecember 29, 1950, Serial No. 203,376

6 Claims. (Cl. 126-91) For a consideration of whatl consider to be novelv and my invention attention is directed to the following specificationand the concluding claims thereof.

In the drawing- Fig. 1 is a schematic view of heating apparatusembodying the present invention.

Fig. 2 is a somewhat enlarged front elevation of the apparatus shown inFig. 1.

Fig. 3 is a somewhat enlarged section on line 3--3 of Fig. 1 with partsomitted.

Fig. 4 is an enlarged section 0n line 4-4 of Fig. 2. In the drawing, 10indicates a portion of the wall of a substantially gastight chamberwherein articles may be heated in a controlled atmosphere, and 11indicates an internally fired U-shaped tube for producing radiant heatin said chamber, the wall of said chamber comprising an exterior metalskin 12 and an interior lining of refractory heat insulating material 13next to said skin. Air at atmospheric pressure ows into the burner end15 of said tube under the inuence of draft applied at the exhaust end ofsaid tube, the draft being produced by a power operated exhauster 16indicated as a blower whose suction is made effective at the exhaust end14 of said tube through a llue gas passage in an air preheater 18 whichforms the special subject of the present invention. A flue pipe 20 isshown as connecting the exhauster 16 with the discharge end of said uegas passage.

The exhaust end 14 of the combustion tube 11 is fixedly secured gastightto the exterior metal skin 12 of the furnace chamber wall 10 by meanscomprising stud bolts 21 mounted on said skin to extend through a rimflange 22 on a collar 23 which is screwed onto the exhaust end 14 ofsaid tube. The burner end 15 of the combustion tube is free to moveaxially relative to said furnace chamber wall 10 so that when thermalexpansion causes relative movement between the two legs of thecombustion tube it will be the burner end of the tube which movesaxially relative to the exhaust end of the tube. -To prevent loss ofatmosphere from the furnace chamber by way of the aperture through whichthe burner end 15 of the combustion tube extends out of the furnacechamber, the burner end of said tube is surrounded by a metal bellows 27of which the end next to the metal skin 12 of the furnace chamber wallis secured gastight to said skin by means comprising stud bolts 28carried by said skin to extend through a rim flange 30 on the adjacentend of the bellows for clamping said flange against said skin. The otherend of the bellows has a rim ange 32 through which stud bolts 31 extendfor securing said flange gastight against the rim flange 33 of a collar34 screwed onto the burner end 15 of the combustion tube, the screwstuds extending from an annular member 36 herein after more fullydescribed.

The air preheater 18 comprises a body 35 mounted on the burner end 15 ofthe combustion tube 11 for movement therewith, the mounting meanscomprising the rim ange 33 against which the annular member 36 isadapted to be clamped by said stud bolts 31, the "said annular member 36being a flange at one end of an annular 2,700,380 Patented Jan. 25, 1955icc wall-37 which defines an air tunnel 38 in front of the burner end 15of the combustion tube. Preheated air enters said air tunnel 38 througha peripheral air gap 43 formed between the outer end of said tunnel andan end plate 40 in front of the outer end of said tunnel and which isspaced from said outer end by spacer elements 41 through which studbolts 42 carried by the body 35 extend. The burner end 15 of thecombustion tube comprises a burner 44 at the end of a supporting tube 45secured to the aforesaid end plate 40. Fuel issuing from the burner 44may be ignited in any preferred way as by a flame from a pilot burner 47shown as extending through an aperture in the said end plate 40.

The said body 35 has a flue gas passage 48 extending therethroughwhereby to constitute said body an internally heated radiator. The inletend 50 of said passage 48 connects with the exhaust end 14 of thecombustion tube to receive hot flue gas therefrom and the outlet end 51of said passage connects with the aforementioned exhauster 16 throughthe connecting flue 20. Said inlet end 50 is defined by a tubular member52 projecting from said body 35 and said member is movably positionedwithin the exhaust end 14 of the combustion tube to permit free axialmovement relative thereto. It is not essential that the joint betweensaid tubular member 52 and the said exhaust end 14 shall be gastight butnevertheless it is desirable to prevent objectional infiltration ofatmospheric air through said joint with consequent cooling of the fluegas flowing into said tubular member 52, and therefore the latter isdesirably surrounded by a ceramic packing sleeve 53 movable with saidmember 52 The flue gas passage 48 may be said to comprise a short legand a long leg, the long leg extending in front of both the exhaust end14 and the burner end 15 of the combustion tube and the short legextending at a right angle to the long leg and being defined by thepassage 50 in tubular member 52. As may be seen in Figs. 3 and 4, thewall 37 which defines the air tunnel 38 in front of the burner end ofthe combustion tube extends across the flue gas passage 48'so that theflue gas ows around said wall to reach the outlet end 51 of the flue gaspassage 48. As may be seen in Figs. 3 and 4, the long leg of the ue gaspassage 48 is rectangular rather than round in section and resembles abox of which the back wall is indicated at 49, the front wall at 67, thebottom wall at 39, the top wall at 55 and one of the end walls at 46, itbeing understood that the walls of the box will be heated by the iluegas flowing through the flue gas passage 48. That portion of the frontwall 67 of the radiator opposite the exhaust end 14 of the combustiontube will be relatively highly heated not only by the flue gas flowingtowards said portion and impinging thereagainst but also by radiant heatfrom such heated parts of the combustion tube as can be seen by saidwall portion.

The long leg or box portion of the radiator 35 is surrounded in spacedrelation by a heat insulated jacket or casing 54 to provide an airchamber 64 for a current of the air to be preheated, the casing havingan air inlet 61 about the neck portion of the tubular member 52 of theradiator and having its outlet 70 extending about the air gap 43 aboutthe outer end of the air tunnel 38 in front of the burner end of thecombustion tube. It will be understood that air at amospheric pressureenters the air inlet end 61 of said jacket or casing 54 by virtue of thedraft or suction prevailing at the burner end of the combustion tube asa result of the draft produced bythe exhauster 16 at the exhaust end ofthe tube. Portions of said radiator jacket 54 are indicated at Sti- 60.Infiltration of cold air at the joint between the rim of the end plate40 and the surrounding portion of said jacket may be prevented by asheet metal wall 65 overlapping said joint, the wall being clampedagainst the end plate 40 by the nuts on the stud bolts 42. Other jointsmay be sealed substantially air tight by asbestos rope packing or thelike as indicated at 66.

The character of the flame in the interior of the return leg of thecombustion tube 11 may be viewed through a peep hole provided by asection of pipe 68 in the front end wall 67 of the radiator coaxial withthe tubular member S2, the outer end of said pipe section being normallyclosed by a pipe cap 69.

For descriptive purposes it has been convenient to describe theinvention as applied to a U-snaped combustion tube 11 but it should beunderstood that the invention is not limited in its application to thattype of tube since it is obvious that the two legs of said tube mightwell be replaced by two independently tired tubes arranged with theexhaust end of one in relatively close proximity to the burner end ofthe other for connection with the radiator 35 as shown in Fig. 4.Moreover, the air preheater per se is not limited in its application toa cornbustion tube since the place where combustion of the fuel takesplace may be defined by walls other than those of a tube and thereforethe air tunnel 38 which extends through the radiator may be consideredas delivering to the burner port of a refractory combustion chamber andthe tubular member 52 of the radiator as being in connection with anexhaust port of said combustion chamber.

The back wall 56, 57 of the air chamber defined by the air casing 54 isspaced a substantial distance from the back wall 49 of the heatradiator; hence the air on entering said chamber through the air inlet61 is free to spread out along the entire area of said back wall 49 ofthe radiator. To insure that the air thus entering at 61 shall not shortcircuit to the air outlet 70 and thus not be properly heated, theexterior peripheral portion of the radiator 35 is provided with a seriesof parallely extending vanes or ribs 24 between which the air must flowin owing from the back portion to the front portion of said air chamberin front of the front wall 67 of said radiator.

From the foregoing description it may now be seen that the presentinvention provides an air preheater that is well adapted for itsintended purpose.

What I claim is:

1. In combustion apparatus, in combination, a front radiator wall havingan aperture, a back radiator wall having an aperture opposite to theaperture in the front wall, a peripheral wall connecting the peripheryof the front wall with the periphery of the back Wall, said front, backand peripheral walls constituting the external walls of the radiator, anannular wall connecting the aperture in the front wall with the aperturein the back wall and forming a tunnel through the radiator, a ue gasinlet tube connected to and communicating with the interior of theradiator on one side of the tunnel, a flue gas outlet tube connected toand communicating with the interior of the radiator on the opposite sideof the tunnel, the radiator being gastight except for the connectionswith such inlet land outlet tubes, a casing disposed about the radiatorin spaced relationship, which encloses an air space surrounding theradiator', and which has an inlet for admitting air to the space betweenthe casing and the front wall of the radiator and is airtight except forsuch inlet, an extension of the radiator tunnel, projecting from thefront wall of the radiator and extending through the casing, the tunneland extension forming an outlet passage to conduct air from the spacebetween the casing and the back wall of the radiator, and a burnerarranged to discharge fuel into the air flowing through such outletpassage.

2. In combustion apparatus according to calim l, a plate forming a partof the casing, opposite the inlet end of the radiator tunnel, andsupporting the burner.

3. In combustion apparatus according to claim 1, a structure wherein theue gas inlet tube is connected to the front wall of the radiator, andthe air inlet of the casing surrounds such flue gas inlet tube.

4. In combustion apparatus according to claim l, a structure wherein theperipheral wall of the radiator is substantially more closely spacedfrom the casing than the front and back walls of the radiator.

5. In combustion apparatus according to claim 1, spaced parallel ribsdisposed between the peripheral Wall of the radiator `and the casing,said ribs extending longitudinally between the front wall and the backwall of` the radiator. 1

6. In combustion apparatus according to claim l, a ring tube connectingthe radiator tunnel extension to the flue gas inlet tube.

References Cited in the le of this patent UNITED STATES PATENTS 408,980Johnson Aug. 13, 1889 964,031 Leahy Iuly 12, 1910 1,151,575 DuchschererAug. 31, 1915 1,244,864 Kemp Oct. 30, 1917 1,288,516 Cole Dec. 24, 19182,146,410 Vaughan Feb. 7, 1939 2,188,133 Hepburn Jan. 23, 1940 2,200,731Woodson May 14, 1940 2,226,816 Hepburn Dec. 31, 1940 2,299,901 JohnstonOct. 27, 1942 2,391,447 Edge Dec. 25, 1945 2,465,711 Clarkson Mar. 29,1949 2,549,093 Huber Apr. 17, 1951

